Apparatus for manufacturing prestressed concrete members

ABSTRACT

A system for casting prestressed concrete members on a highly automated, mass production basis. The system employs a plurality of portable molds, each of which defines a hollow mold cavity. The portable molds are preferably substantially identical in construction, include open top portions through which charges of concrete mixture can be directed into the mold cavities, and further include means for releasably securing lengths of reinforcing strand in a selected arrangement within each mold cavity. Conveying means carry a plurality of molds simultaneously along a predetermined path of travel through operating stations adapted to subject each mold to a series of successive operations. A mold cleaning and oiling station cleans the interior surfaces of each mold cavity and coats the interior surfaces with a releasing agent. An placement station inserts hardware into the mold cavities, to be cast within the concrete members. A strand placement station emplaces predetermined lengths of reinforcing strand within the mode cavities, and a tensioning station applies a selected pretensioning force to the reinforcing strand. Filling and compacting stations successively feed a measured charge of concrete mixture into each of the molds and compact the concrete charge in the molds. Means are provided to cure the concrete charge within each of the molds after the filling and compacting operations are completed. Conveyor means receive and convey a plurality of the molds simultaneously along a predetermined path of travel after the curing operation is completed. A tension releasing station operates to release the pretensioning load on the reinforcing strand emplaced within each of the molds. Means are provided downstream from the tension releasing station for preparing the molds for the removal of the cast concrete members. A demolding station operates to remove the cast concrete member from each mold. Means are also provided to finish the demolded concrete members and to prepare the empty molds for recirculation through the manufacturing system. In the preferred embodiment each operating station is provided with a portable mold, and the operating stations perform their respective operations substantially simultaneously, within a selected time interval.

United States Patent [72] Inventors Stanley V. Margolin Auburndale; Paul W. Glaser, lslington; Leonard V. Gallagher, Wollaston, Mas. [21] Appl. No. 721,834 [22] Filed Apr. 16, 1968 [45] Patented May 4, 1971 [73] Assignee Arthur D. Little, Inc.

Cambridge, Mass.

[54] APPARATUS FOR MANUFACTURING PRESTRESSED CONCRETE MEMBERS 16 Claims, 40 Drawing Figs. [52] US. 25/2, 25/41 264/228 [51] Int. Cl B28b 15/00, 1328b 23/06 [50] Field ofSearch 25/2, 118 (T), 41.1; 254/295; 264/228 [56] References Cited UNITED STATES PATENTS 3,006,053 10/1961 Miller 25/ (Mold Cleaning Digest) 3,118,211 1/1964 Baber.... 25/118(T) 3,128,521 4/1964 Baker 25/118(T)X 3,163,904 1/1965 Ziolkowskr 24/ 126 3,207,829 9/ 1965 Nieber 264/228 3,230,561 1/1966 Taccone.... 25/ (Mold Cleaning Digest) 3,274,659 9/1966 Baker 9 25/2 3,281,911 11/1966 Baker.... 25/118(T) 3,305,907 2/1967 Baker.... 25/2 3,384,939 5/1968 Baker 25/2 Primary Examiner]. Spencer Overholser Assistant Examiner-Ben D. Tobor Attorney-Hume, Clement, l-Iume and Lee 1, Hun

o o b ABSTRACT: A system for casting prestressed concrete members on a highly automated, mass production basis. The system employs a plurality of portable molds, each of which defines a hollow mold cavity. The portable molds are preferably substantially identical in construction, include open top portions through which charges of concrete mixture can be directed into the mold cavities, and further include means for releuably securing lengths of reinforcing strand in a selected arrangement within each mold cavity. Conveying means carry a plurality of molds simultaneously along a predetermined path of travel through operating stations adapted to subject each mold to a series of successive operations. A mold cleaning and oiling station cleans the interior surfaces of each mold cavity and coats the interior surfaces with a releasing agent. An placement station inserts hardware into the mold cavities, to be cast within the concrete members. A strand placement station emplaces predetermined lengths of reinforcing strand within the mode cavities, and a tensioning station applies a selected pretensioning force to the reinforcing strand. Filling and compacting stations successively feed a measured charge of concrete mixture into each of the molds and compact the concrete charge in the molds. Means are provided to cure the concrete charge within each of the molds after the filling and compacting operations are completed. Conveyor means receive and convey a plurality of the molds simultaneously along a predetermined path of travel after the curing operation is completed. A tension releasing station operates to release the pretensioning load on the reinforcing strand emplaced within each of the molds. Means are provided downstream from the tension releasing station for preparing the molds for the removal of the cast concrete members. A demolding station operates to remove the cast concrete member from each mold. Means are also provided to finish the demolded concrete members and to prepare the empty molds for recirculation through the manufacturing system. In the preferred embodiment each operating station is provided with a portable mold, and the operating stations perform their respective operations substantially simultaneously, within a selected time interval.

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INVENTDRS STANLEY v. Mum/1v, HUI. m GLJSER 4ND [IO/MRO V GMMGIIER WW, 2m): f /rmeaade JTTMNEYS 3 NQ S V @ATENTEDMAYMQ?! 3.577310 SHEET 12 [1F 12 mvnvrons STANLEY u MARGOLIN, PAUL n. GLASER AND LEONARD l. GALLAGHER ITTORIVEYS .i n; i -l QONCRETE MEMB RELATED APPLICATIONS The invention disclosed and claimed herein relates I generally to the inventions disclosed and claimed in the appliand the application of William P. Hidden, entitled Portable Molding Apparatus," Ser. No. 721,767, each of which was filed concurrently and commonly assigned with the present application.

7 BACKGROUND AND SUMMARY OF THE INVENTION This invention generally relates to a system for manufacturing prestressed concrete members, such as concrete railway ties, concrete beams and the like, on an automated mass production basis.

Prestressed concrete members are being employed in many industrial applications at the present time, such as in the railroad, building construction and road building industries, because of the inherent structural qualities of such members. However, many systems now used to make concrete members are small scale, labor-intensive operations. Such systems, involving a high degree of direct labor, substantially increase unit cost of the concrete members, often to the point where the members cannot compete effectively with other forms of structural components. Moreover, such systems often include expensive or poorly designed equipment which materially reduces the efiiciency of the system and which prevents the continuous manufacture of a concrete member which is reproducible within closely held specifications. It is thus apparent that the use of prestressed concrete members would be more prevalent, and concrete members could compete more effectively with other types of structural members such as steel or wooden members, if more efficient and economical systems could be employed to manufacture the concrete members.

In an attempt to solve the above problems, the present invention provides a manufacturing system which permits prestressed concrete members to be made economically, with a minimum need for direct labor. The system of the present invention also allows the concrete members to be manufactured rapidly, on a mass production basis, while permitting the product to be reproduced within closely held specifications.

To accomplish the above objectives, the system in accordance with this invention provides integrated apparatus which cast a prestressed concrete member in each of a plurality of substantially identical portable molds with a minimum of direct labor. Each portable mold defines an open mold cavity of a desired configuration for receiving a charge of concrete mixture and includes meams for suspending lengths of pretensioned reinforcing strand through the mold cavity in a desired pattern. in the preferred embodiment each mold is provided with movable end assemblies, defining the end portions of the mold cavity, which include means for securing the reinforcing strand within the mold cavity and for applying a desired pretensioning force to the strands. The movable end assemblies of the preferred form of mold can be spaced away from the adjacent end portions of the mold, to thereby facilitate the cleaning of the molds, the placement and pretensioning of the reinforcing strand, and the demolding of the completed concrete members.

The system of the present invention further includes means to convey a plurality of the portable molds simultaneously along a predetermined path of travel. The mold conveying means is arranged to carry each mold through a successive series of operating stations which cooperate to form a concrete member of the desired configuration within each mold. Briefly, the operating stations positioned along the path of travel of the conveying means operate to successively clean and oil each mold; emplace reinforcing strand and other hard ware within each mold cavity; apply a selected pretensioning force to the reinforcing strands; fill each mold cavity with a measured charge of concrete mixture; and compact the concrete charge within the mold cavity. The molds are thereby prepared for treatment at a curing station, where the concrete in each mold is hardened around the reinforcing strands to form the desired prestressed concrete member.

The system of the present invention also provides means for demolding and finishing the cured concrete members. in this regard, the system includes a second conveyor means adapted to carry each mold through an additional series of operating stations following the concrete curing operation. The additional stations successively release the pretensioning force on the reinforcing strands; demold the completed concrete members; and finish the concrete members by removing excess strand. Means are also provided to orient the empty portable molds for recycling through the system. Finally, in the preferred embodiment the system is arranged to conduct the operations of the stations substantially simultaneously, within a selected time. By such an arrangement, the system when in continuous operation will function to prepare concrete members for curing, and will demold completed members, within a selected short interval of time.

EXEMPLARY EMBODTMENT The exemplary embodiment of the manufacturing system in accordance with this invention is particularly adapted for casting a concrete railway tie of current design. in this regard, the current specifications of the American Association of Railroads require the exemplary concrete tie to be prestressed by four lengths of reinforcing strand in a manner which applies a 100,000 pound pretensioning load to the tie. The pretension ing load is further required to be equally distributed among the four strands, at 25,000 pounds per strand. in addition, inserts for receiving rail fastening hardware are to be cast within the rail pad area of the concrete ties.

0f course, although the exemplary embodiment is particularly adapted to manufacture concrete railway ties on a highly automated mass production basis, it will be recognized by those skilled in the art that the present invention is readily adaptable for use in making other types of prestressed concrete units, with substantially the same degree of accuracy and speed.

Additional features and advantages of the invention will be more fully understood by considering the following description of an exemplary embodiment thereof, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a mold inspection station incorporated in the concrete casting system embodying the features of the present invention;

FIG. 2 is a cross-sectional view of one stage of a mold cleaning and oiling station incorporated in the system, which operates to abrade and clean the end portions'of the cavity defined by a portable mold;

FIG. 3 is a cross-sectional view of an additional stage of the mold cleaning and oiling station, which operates to abrade and clean the interior sidewalls of a mold;

FIG. 4 is a cross-sectional view of a further stage of the mold cleaning and oiling station, which operates to abrade and clean the bottom wall of a mold;

H6. 5 is a cross-sectional view of a further stage of the mold cleaning and oiling station, which operates to remove loosened dust and debris from the cavity of a mold;

FIG. 6 is a cross-sectional view of the oiling stage of the mold cleaning and oiling station, which operates to apply a suitable releasing agent to the interior surfaces of a cleaned mold cavity;

FIG. 7 is a cross-sectional view of an insert placement station incorporated in the system in accordance with this invention which operates to place rail fastening inserts within the mold body;

ing strand in a desired pattern within the mold;

FIG. 9 is a cross-sectional view of the initial stage of a strand tensioning station incorporated in the system, which operates to apply a selected pretensioning force to two diametrically opposed reinforcing strands emplaced within the mold;

FIG. III is a cross-sectional view of a second stage of the strand placement station incorporated in the system, which operates to apply a selected pretensioning force to the two remaining diametrically opposed reinforcing strands within the mold;

FIG. II is a cross-sectional view of the final stage of the strand tensioning station incorporated in the system, which operates to apply a final tensioning force tothe reinforcing strands;

FIG. 12 is a cross-sectional view of a filling station incorporated in the system, illustrating a mold in position to receive a measured charge of concrete mixture within the cavity of the mold body;

FIG. I3 is a cross-sectional view of a compacting station incorporated in the system, illustrating a filled mold positioned for compaction of the concrete charge;

FIG. I4 is an elevational view of a mold positioned at the final stage of the strand tensioning station, as viewed along the line I4I-I4l in FIG. Ill;

FIG. I5 is a plan view of a mold positioned at the final stage of the strand tensioning station, as viewed along the line -15 -in FIG. I l;

, FIG. It is an elevational view of the filling station incorporated in the system of the present invention, as viewed along the line lid-I6 in FIG. I2;

FIG. I7 is a plan view of the mold filling station, as viewed along the line 17-17 in FIG. Id;

FIG. I3 an elevational view of the compacting station ineluded in the system of the present invention, as viewed along the line lh-lld in FIG. I3;

FIG. I9 is a plan view of the compacting station, as viewed along the line I9-I9 in FIG. I3;

FIG. 26) is a schematic cross-sectional view illustrating a filled mold in transit from the compacting station illustrated in FIGS. I3 and III to a suitable concrete curing stan'on such as shown in FIG. 2i;

FIG. 21 is a schematic illustration of a concrete curing station, showing a plurality of filled molds stacked in preparation for curing of the concrete charged into the molds;

FIG. 22 is a schematic illustration of the concrete curing station, showing a mold prepared to be discharged from the station after the curing cycle has been completed;

FIG. 23 is a cross-sectional view of a strand tension releasing station incorporated in the system, which operates to release the pretensioning force on the reinforcing strands after the concrete in the mold body has been cured;

FIG. 24 is a cross-sectional view of a mold turnover station incorporated in the system, which operates to orient the mold to permit the demolding of the cured concrete member;

FIG. 25 is a cross-sectional of a demolding station included I in the system in accordance with the present invention which operates to remove the cured concrete member from the mold;

FIG. 26 is a cross-sectional view of a finishing station in- I eluded in the system, which operates to finish the cured concrete members by removing the excess lengths of. reinforcing strands from the ends of the concrete members;

FIG. 27 is a cross-sectional view of a mold turnover station included in the system, which operates to return the empty mold body to an upright position in preparation for recycling the mold through the manufacturing system;

FIG. 23 is a partial elevational view of the tension releasing station as viewed along the line 28 in FIG. 23, illustrating the condition of the station at the beginning of the tension releasing operation;

' FIG. 29 is a partial plan view of the tension releasing station, as viewed along the line 23-29 in FIG. 28;

FIG. 30 is a partial elevational view of the tension releasing station illustrated in FIGS. 23, 23 and 29, showing the condition of the station after the initial strand tension releasing step has been completed;

FIG. 31 is a partial elevational view of the releasing station shown in FIG. 30, illustrating the condition of the station after the pretensioning force on the strands has been released;

FIG. 32 is a partial elevational view of the releasing station illustrated in FIGS. 30 and 31, showing the releasing station condition after the station has been operated to extend the adjacent movable mold end plate assembly away from the mold body;

FIG. 33 is a cross-sectional view of the releasing station and movable mold end plate assembly, taken along the line 33-33 in FIG. 32;

FIG. 34 is an elevational view of the mold turnover station, as viewed along the line lid-34 in FIG. 24;

FIG. 35 is a plan view of the mold turnover station, as viewed along the line 35-33 in FIG. 24!; I

FIG. 36 is an elevational view of the mold turnover station, as viewed along the line 36-36 in FIG. 2d;

FIG. 37 is an elevational view of the demolding station included in the system in accordance with the present invention, as viewed along the line 37-37 in FIG. 25;

FIG. 33 is a partial plan view of a demolded concrete member positioned at the demolding station, as viewed along the line 38-38 in FIG. 37;

FIG. 39 is an elevational view of the finishing station, as viewed along the line 39-39 in FIG. 26; and

FIG. 40 is a partial plan view of the demolded concrete member positioned at the finishing station, as viewed along the line in FIG. 39.

Referring generally to the drawings, the portable molds employed in the system in accordance with this invention are indicated by the reference numeral Itltl. Each mold m0 defines a mold cavity having an open top portion which permits the mold to receive a charge of concrete mixture, insert hardware, and reinforcing strand. As shown in FIG. 17, in the preferred embodiment each mold includes movable left and right mold end assemblies, generally indicated by the reference numerals I20 and 140, respectively. The end assemblies and are adapted to be movable from a closed position against the adjacent end of the mold IIIII as illustrated in FIG. Id, where the assemblies define the end portions of the mold cavity, to an extended or opened position, such as illustrated in FIGS. 35 and 36. Each mold IIII) is reinforced transversely by a series of reinforcing struts 1M, and is reinforced longitudinally by a pair of elongate compression tubes 1%.

The construction and operation of the preferred form for the movable mold end assemblies 120 and MI) are fully described in the copending application of Hidden and Yetman, Ser. No. 721,793. Briefly, the left end assembly I20, as shown in FIGS. I5 and 35, includes an end plate 122 adapted to engage with and close the adjacent end of the mold Itltl. Guide rods I23 extend into the adjacent ends of the compression tubes I06 to join the end plate I22 to the body of the mold 1%. A chuck plate I24, spaced outwardly from the end plate 122, includes a plurality of strand receiving chucks I26 which are adapted to receive and releasably grip the adjacent free ends of reinforcing strands S placed within the mold. A pair of mounting pins I25 operated to slidably connect the chuck plate 1124 to the end plate 122. A tension post 123 is connected to the chuck plate 1241 and is capable of receiving an outwardly directed pulling force. The application of a suffieient pulling force to the post I28 will separate the chuck plate 12A from the end plate I22 and thereby apply a tensioning force to reinforcing strands S.

As shown in FIG. 14, the right mold end assembly MAI similarly includes an end plate M2 which engages with and closes the adjacent end of the mold I00. Guide rods M3 extend into the compression tubes I06 to movably join the plate I42 to the body of the mold ltltl. A chuck plate I is positioned adjacent the end plate M2 and includes a plurality of releasably grip the adjacent free ends of the reinforcing strand system. The longitudinal position for the station 250 is selected so that the conveyor200 places each mold 100 at the S.'Mounting pins 145 join the chuck plate 144 to the 'end plate 142 and permit the plates to slide with respect to each other.

A tensioning post 148 attached to the chuck plate 144, is provided to perform the same function for the end assembly 140 as the post 128 performs for the other end assembly 120.

As explained further in the copending Hidden and Yetman application, Ser. No. 721,793, the end assemblies 120 and 140 also include slidable locking plates 130 and 150, respectively, for controlling the function of the assemblies during the concrete casting operation. More specifically, the locking plate 150 is engaged between the end plate 142 and chuck plate 144 within a two-stepped recess 147 (FIG. 33). By-this arrangement, the vertical position of the locking plate 150 can be varied to engage the adjacent end plate 142 and chuck plate 144 at three different positions. The plate 150 can thereby function to maintain the plates 142 and 144 spaced apart at three selected distances. The locking plate 130 is similarly arranged between the plates 122 and 124 of the left end assembly 120. In addition, the locking plate 130 can be arranged to space the plates 122 and 124 at either two or three selected distances.

As explained in application Ser. No. 721,793, the end as semblies 120 and 140 are arranged so that the strand chucks 126 and 146 are deactivated or unlocked by suitable means, such as bushings 121 and 141 (FIGS. and 29), when the locking plates 130 and 150 are in their lowest operating position (FIG. 33). Under such conditions the end and chuck plates of the end assemblies are closely spaced. When the plates 130 and 150 are raised to their second positions, the adjacerit end and chuck plates are separated and the bushings 121 and 141 are disengaged from the chucks 126 and 146. The chucks 126 and 146 are thereby arranged in a ready" condition, prepared for gripping the strands S. Movement of the plates 130 or 150 to their uppermost locked" position further separates the adjacent end and chuck plates and causes the strands S to be elongated a measured amount to compensate for the strand pretensioning force which is lost when the chucks I26 and 146 seat on the strands S.

Referring to FIGS. 1--15, the system in accordance with the present invention includes a horizontal conveyor 200 which defines a path of travel for the portable molds 100.

- Conveyor 200 is adapted to support a plurality of portable molds 100 spaced longitudinally along its length. Suitable power means (not shown). preferably an intermittent drive, is arranged to drive the conveyor 200 through the various operating stations of the system which precede the concrete curing operation. In the preferred embodiment the conveyor 200 places a portable mold 100 at each operating station so that the functions of all of the stations can be performed simultaneously, within a selected time interval.

As illustrated in FIGS. 1-15, the mold conveyor 200 comprises a pair of continuous parallel drive chains 202 which are provided with a plurality of mold-receiving saddles 204. In the exemplary embodiment, the opposed saddles 204 on the chains 202 are adapted to receive and support the bottom portion of a mold 100 which is configured to cast the current form of concrete railway tie. Further, the saddles 204 are uniformly spaced along the longitudinal length of the drive chains 202 at predetermined intervals. A pair of channel-shaped chain tracks 206, supported by a frame structure 210, guide the parallel drive chains 202 throughout the length of the conveyor 200. As seen from FIGS. 14 and 15, the conveyor 200 also includes a pair of parallel roller beds 208 formed from a plurality of longitudinally spaced and transversely extended rollers. The roller beds 208 are positioned to engage with and support the bottom surface of the molds 100 as the molds are carried along the path of the conveyor 200.

As illustrated in FIG. 1, the exemplary embodiment of the system includes an inspection station 250. This station 250 is positioned at an open space at the front end of the conveyor 200 and precedes the operating stations included in the station 250 for a time interval sufficient to permit visual insp'ection of a h mold. By such an arrangement, each of the molds can be examined by an operator at station 250, to

check for damage or improper assembly, before the molds are carried through the subsequent operating stations of the system.

A mold cleaning and oiling station 300 is the first operation station included in the system of the present invention. As seen in FIGS. 2-6, the station 300 is positioned adjacent the conveyor 200 longitudinally downstream from the' abovedescribed inspection station 250. Generally, the operating station 300 includes a series of substations 300A-E which successively engage with each portable mold 100 to clean and oil the internal wall portions of each mold. Thus, the station 300 operates to prepare the cavity of each mold for receiving a fresh charge of concrete mixture at subsequent operating station'of the system.

The preferred form for the mold cleaning and oiling station 300, as illustrated in FIGS. 2 through 6 of the drawings, is more fully described in the above-mentioned copending application of Messrs. Hidden and Hunt, Ser. No. 721,808. Briefly described, each of the operating substations 300A through 300E includes an elevator mechanism designed to intercept the molds 100 as the molds are conveyed along the path of the conveyor 200. The elevator mechanisms at substations 300A- -E are longitudinally spaced along the conveyor 200 in a manner which allows the conveyor 200 to position a mold 100 at each of the substations simultaneously. Thus, the elevator mechanisms can be operated to raise the associated mold 100 from the conveyor 200 so that the operations of the substations can be performed simultaneously.

Referring to FIGS. 2 through 6 in more detail, the elevator mechanism included in each of the substations 300A-E comprises a pair of elevator platforms 302 which are transversely aligned at a selected location along the path of the conveyor 200. In the preferred arrangement each platfonn 302 is positioned along the outside of the conveyor 200, closely adjacent the associated conveyor drive chain track 206. Each platform 302 includes a roller bed 304 adapted to receive and support a mold 100 as the mold is carried into the operating substation. Moreover, each platform 302 is connected to a hydraulic lift cylinder 306 which controls the vertical positioning of the platform 302 curing the operation of the associated substation. Guide rods 308 are included in each elevator mechanism to guide the' vertical movement of the elevator platforms 302. The substations 300A-E also include means to control the longitudinal and transverse positioning of the molds 100. in this regard, each elevator platform 302 is provided with-a longitudinally arranged cam track 310, and each substation 300A-E includes a pair of downwardly-directed spacing brackets 312. As illustrated in FIGS. 2 through 6, the cams 310 are designed to engage with the mold 100 as the mold approaches each of the substations, to thereby align the mold in the desired transverse position. Similarly, the brackets 312 engage with the mold 100 as the mold is elevated by the operation of the cylinders 306, to align the molds into the desired longitudinal position at each substation.

In operation, the hydraulic cylinders 306 initially maintain the elevator platforms 302 in a lowered position at each substation 300A-E, with the roller beds 304 horizontally aligned with the conveyor rollers 208. The saddles 204 of the conveyor 200 can thereby carry a mold 100 onto the pair of roller beds 304 at each substation. The lift cylinders 306 then can be actuated by suitable hydraulic control means (not shown) to raise the associated mold 100 from the mold saddles 204. The cylinders 306 thereby raise a mold 100 into operating position at each of the substations 300 through 30013, as shown in FIGS. 2-6, so that the cleaning and oiling functions of the substations can be initiated. In the preferred arrangement the hydraulic control for the cylinders 306 is arranged to raise all of the elevator platforms 302 in unison, so that the substations A-E will function simultaneously, with a different mold 100 at each substation. Further, is preferred that the stroke 'of all of the cylinders 34% be substantially the same .to facilitate the completion of the operation of each substation 3tltlA-E within the same selected time interval. After 'the operation of each substation is completed, the operation of the hydraulic cylinders 3 is reversed, and the mold 100 is lowered into the adjacent saddle 204 of the conveyor 200. The conveyor can then operate to carry the mold to the following substation or to subsequent operating stations of the system.

As more fully described in the copending Hidden and Hunt application, Ser. No. 721,808, the substation A is adapted to abrade and clean the interior surfaces of the end walls of each mold 1%. As seen in H0. 2, the substation A accordingly includes a pair of cleaning heads 316, only one of which is shown. A pair of longitudinally arranged beams 314A (only one of which is shown) support the heads 316 adjacent the conveyor 2th) in a position directly above the elevator platforms 302 of substation 300A. A universal joint 3R8 connects each head 316 to the beam 314 in a manner which permits the head to oscillate longitudinally and transversely with respect to the conveyor 234) during the operation of substation 300A.

Each cleaning head 3% includes a rotatable brush 320 for engaging with the interior end portions of the mold 100, to thereby remove dust and debris from the mold end portions. Each head 316 also can be provided with a collecting means such as a vacuum mechanism (not shown), for collecting the dust and debris removed from the mold 100 by the rotating brushes 320. Suitable means (not shown) are also provided to oscillate the brushes 320 longitudinally and transversely during the operation of substation 306A, to assure that the end portions of the mold we are thoroughly cleaned. As explained in the Hidden and Hunt application Ser. No. 721,808, the operation of substation 300A is further facilitated by arranging'the mold end assemblies 120 and 140 in their open positions (see H6. 34) at substation A so that the brushes 320 can readily clean the adjacent end portions of the mold body 1%.

, Referring to FIG. 3, the cleaning substation 300B is adapted to abrade and clean the interior sidewalls of the molds 100. As explained more fully in the copending application of Hidden and Hunt, this sidewall cleaning operation is accomplished by providing the substation 3008 with a translating cleaning head 322. As shown in H6. 3, the head 322 is suspended above the conveyor 2% at substation B by a transverse frame member 3148. Suitable brackets 324 slidably join the cleaning head 322 to the member 3148 in a manner which permits the head 322 to translate transversely across the conveyor 2%. The head 322 includes a pair of rotatable conicallyehaped brushes 326 which are designed to engage with and abrade the interior sidewalls of each mold Will. Additionally, the substation B includes a collecting means, such as a vacuum hood .328 which extends over the cavity of the mold 100 when the mold is raised by the cylinders 3%. Suitable means (not shown) are also provided to translate the head 322 across the conveyor 2%.

As illustrated in H6. 3, when the substation I operation the brushes 3 of the head 322 will engage with and abrade the interior wall surfaces of the mold W0. Moreover, the translation of the head 322 across the conveyor 2% brings the brushes 326 into engagement with the mold sidewalls throughout the entire length of the mold 100. The vacuum hood 323 operates simultaneously with the head 322 and collects the major portion of the dust and debris loosened from the mold sidewalls by brushes 326.

. h the bottom wall of each mold 1%. Means (not shown) operate to translate the head 330 transversely across the conveyor 2% to bring the brush 334 into engagement with the mold bottom substation 300D is also described The substation is operative to abrade and clean the interior bottom wall of each mold W0, as set forth in the aboveidentitied Hidden and Hunt application Ser. No. 72l ,808. As shown in FIG. 4, the substation 3 includes a cleaning head 33!) which is movably mounted to a transverse supporting beam 3114C by means of a sliding bracket 332. The head 330 forcibly rotates a brush 334 which is wall along the full length of the mold 100. Substation 300C also includes a collection mechanism such as a vacuum hood 336 to remove the major portion of the loosened dust and debris from the cavity of the mold 100.

ln operation, the hydraulic cylinders 306 at the substation 3 raise the mold 104) from the conveyor 200 and bring the brush 334 into engagement with the mold bottom wall. The head 330 then rotates the brush 334 and simultaneously translates the brush transversely across the conveyor 200. Accordingly, dust and debris stuck to the bottom wall of the mold cavity is forcibly removed by the brush 334 along the full length of the mold nos. At the same time, the vacuum hood 336 is activated to remove the major portion of the dust and debris loosened from the mold by the brush 334.

Referring to FIG. 5, the operating substation 330D is adapted to collect and remove any dust and debris from the interior surfaces of the mold cavity which may remain after the abovedescribed mold cleaning operations are completed. To accomplish this result, the substation 300D includes a vacuum head 338 which is slidably supported on a transverse frame structure 314D by means of sliding brackets 342. The vacuum head 338' is connected to a suitable high-powered vacuum source (not shown) by means of a conduit 340. As seen in FlG. 5, the vacuum head 338 is designed to fit within the cavity of the mold 100, in close relationship to the interior wall portions of the mold, when the mold is elevated, at the substation 300D. During the operation of the substation 300D, the vacuum head 338 is translated transversely across the conveyor 2410 by suitable means (not shown) so that the head forcibly collects the dust and debris accumulated within the cavity of the mold 100. The construction and operation of in detail in the copending Hidden and Hunt application.

The final substation 300E of the cleaning and oiling station 300 is designed to uniformly coat the interior surfaces of the mold cavity of each mold 100 with a suitable releasing agent. As shown in FIG. 6, the substation 300E accordingly includes a spraying head 334 which is movably supported on a transverse frame member 314E by means of sliding brackets 348. The head is designed to be freely received within the cavity of the mold 100, and includes a plurality of nozzles 346 arranged to direct a spray of releasing agent onto all of the interior wall surfaces of the mold. During operation of the subs tation 300E the head 344 is translated across the conveyor 200 by suitable means (not shown) so that the head traverses the full length of the mold W0. The interior surfaces of the mold we are thereby uniformly coated with a suitable relea ing agent which will facilitate the following operations of system. The construction and operation of substation 300E is again more fully tion Ser. No. 721,808.

As set forth above, the exemplary embodiment of the present invention comprises a system for manufacturing a current form of concrete railway tie. At the present time, the specifications of the American Association of Railroads require that each of the concrete ties be providedv with threaded inserts at the rail pad area for receiving the fastening means which holds the rails in correct position on the tie. Accordingly, as illustrated in FIG. 7, the exemplary embodiment of the system is provided with an insert placement station 35%. Station 350 is positioned adjacent the conveyor 200 immediately downstream from the cleaning and oiling station 300, and is adapted to automatically place the desired number of rail-fastener inserts within the cavity of each mold 104).

Referring to FIGS. "7 and K5 in detail, the inserts to be placed within the interior of each mold 1% in the illustrated embodiment are schematically illustrated by the cylindrical bodies 370. The inserts 370 have internally-threaded openings for receiving threaded bolts which are typically used to fasten designed to engage with v rails to concrete ties. As shown in FIG. 15, two inserts 370 are described in the Hidden and Hunt Applica- 9 to be placed within themold 100 at each of two raised bosses 102 which are provided to define the rail pad area of the cast i railway tie. As seen in FIG. 7, each mold 100 includes a pair of In accordance with the present invention, the insert placement station 350 includes means to automatically place the inserts 370 upon the studs 105 in each of the molds 100. ln this regard, the station 350 is provided with a placement head 366 which is mounted upon a transverse supporting member 364.

. As seen in FIG. 7, the head 366 comprises a storage compartment 367 within which a supply of inserts 370 can be stored. The head 366 further includes four funnel nozzles 368, only one of which is illustrated in P16. 7. The nozzles 368 are in communication with the storage compartment 367 and are spaced transversely across the conveyor 200 in a pattern which corresponds to the spacing of the insert studs 105 on the portable molds 100. Accordingly, a supply of inserts 370 can flow downwardly from the compartment 367 into the nozzles 363, and the noules 368 will in turn direct the inserts downwardly toward the studs 105 in the mold 100. Suitable means (not shown), such as a vibrating mechanism or the like, is joined to the head 366 to orient the inserts 370 within the compartment 367, and to feed each insert 370 into the nozzles 368 in the desired direction, such as illustrated in FIG. 7. In addition, gating means (not shown) are provided within the head 3% to control the discharge of the inserts 370 from the nozzles Of course, other types of vibrating feed hoppers such as the head are available or can be devised by those skilled in the art without departing from the present'invention.

The insert placement station 350 also includes an elevator mechanism to raise each of the molds 100 into engagement with the insert placement head 366. Station 350 is thus provided with a pair of elevator platforms 352 which are transversely aligned adjacent the conveyor 200. Each platform 352 includes a roller bed 354 for supporting the mold 100, and each platfonn is supported by a hydraulic actuating cylinder 356. Guide rods 353 control the positioning of the platforms 352 when the cylinders 356 are actuated. Further, the elevator platforms 352 have a cam track 360 for engaging with each of the molds 100 as the mold is conveyed to the station 350, to orient the mold into the desired transverse position. The station 350 also includes brackets 362 which engage with the mold 100 as the elevator platforms 352 raise the mold 100 upwardly from the conveyor 200. The brackets 362 thereby control the longitudinal positioning of the molds 100 at the station 350.

The operation of the insert placement station should be apparent from the above description of the exemplary embodiment of the station. At the start of the insert placement operation the elevator platforms 352 are vertically arranged, by means of cylinders 356, so that the roller beds 354 are in horizontal alignment with the roller beds 208 of the conveyor 200. The insert placement station 350 will thereby receive the mold 100 being carried by the conveyor 200. As a mold 100 approaches the station 350 the mold engages with the cam tracks 360 on the elevator platforms 352 and is thereby arranged into the desired transverse position with respect to the insert head with the mold 100 positioned on the roller beds 354, the cylinders 356 are actuated by a hydraulic control system (not shown) to raise the mold 100 into a position adjacent the insert placement head 366, such as seen in H0. 7. The brackets 362 engage with the rising mold 100 and orient the mold into the desired longitudinal position with respect to the head With the mold 100 in the raised position as shown in FIG. 7, the head 366 can be actuated, as described above, to place an insert 370 onto each of the studs 105 in the mold. The actuation of the hydraulic cylinders 356 can then be reversed to return the mold to the-mold saddle 204 on the conveyor 2 00. The mold 100 is thereby prepared for movement by the conveyor 200 into the subsequent operating stations of the system. As'seen in FIG. 7, the stroke of the cylinders 356 at the station 350 is preferably substantially the same as the stroke for the cylinders 306 of the preceding station 300. Such an arrangement facilitates the completion of the operation of the station 350 within the same selected time interval as needed for the operation of the mold cleaning and oiling substations A-E. Of course, it will be appreciated by those skilled in the art that the station 350 can be adapted to place other types of hardware within the cavity of the mold 100 in substantially the same manner that the station operates with respect to the railway tie inserts 370.

As illustrated in H6. 8, the system of the present invention also includes a strand placement station 400, positioned adjacent the conveyor 200 downstream from the insert placement station 350. The station is adapted to automatically feed the desired lengths of reinforcing strands S transversely across the path of the conveyor 20 and to place the strands S in a predetennined arrangement within the cavity of the mold 100. In the exemplary embodiment, the station 400 operates to place four lengths of reinforcing strand S within each of the portable molds 100 in a manner which satisfies the specifications of the American Association of Railroads for the current form of reinforced concrete railway tie.

The preferred form of strand placement station is fully described in the above-mentioned copending application of Messrs. Hidden and Yetman, Ser. No. 721,793. Briefly, the placement station 400 includes a channel-shaped placement head 416 which is slidably supported on a transverse beam 414 by brackets 418. A hydraulic piston 422, schematically illustrated in H6. 8, is provided to control the transverse positioning of the head 416 with respect to the mold 100 during the strand placement operation. The head 416 also includes an array of channels420 for receiving lengths of reinforcing strands S. The channels 420 are arranged in a predetennined pattern and preferably extend the full length of the placement head 416. A releasable support member 424 is adapted to close against the lower portion of each of the channels 420 to temporarily maintain a strand S within each channel.

As fully described in the copending application of Messrs. Hidden and Yetman (Ser. No. 72l,793), the placement station 400 includes a suitable feeding apparatus (not shown) which feeds the reinforcing strands S transversely across the conveyor 200 into the channels 420. During such strand feeding, the members 424 are closed against the channels 420, as shown in FIG. 8, so that the strands S are temporarily supported within the channels, The strand feeding continues until a desired length of strand S is within each channel 420, and a free end of the strands projects beyond each end of the channel. Suitable limit switches or the like (not shown) can be included on the head 416 to stop the strand feeding operation after the desired strand lengths are fed into the channels 420. If the strand is being fed into the head 316 from a continuous source, a suitable cutting device (not shown) also can be provided at the station 400, to cut each of the strands S to the desired length.

The placement station further includes a pair of aligned elevator platforms 402 (only one of which is shown) for raising the portable molds 100 from the conveyor 200 into engagement with the placement head 616. Each platform 402 has a roller bed 404 for receiving the molds 100 as the molds are carried along the path of the conveyor 200. A hydraulic actuating cylinder 406 and guide rods @108 control the vertical positioning of the elevator platforms 402 and roller beds 4% during the operation of the station 600. Each platfonn 402 also has a cam track 410, as shown in FlG. 3, positioned for engagement with the molds 100. The tracks 410 control the transverse positioning of each mold 100 with respect to the placement head 416. The station 400 also includes brackets 412 which engage with the molds 100 and control the longitudinal positioning of the molds with respect to the head 416.

, In the preferred embodiment, the molds 106 are positioned on the conveyor 21111 so that the movable'mold end assemblies 120 and.140 are maintained in an open position (FIG. 35) as the moldsare carried to the station During the operation of the placement station the elevator platforms 402 are vertically arranged by the hydraulic cylinders 406 so that the roller beds 404 are in horizontal alignment with the roller beds 208 on the conveyor As a mold 100 is carried toward the stations by the conveyor 200, the mold engages with the cam tracks 410 and is thereby aligned transversely with respect to the placement head 416. The mold 100 further becomes positioned on the roller beds of the elevator platforms 402. Simultaneously with the movement of the mold 100 into the station 460, the strands S are fed into the channels' 420 of the placement head 416 in the above-described manner. Also, the hydraulic piston 422 is activated by suitable control means (not shown) to move the head 416 transversely into a predetermined position above the conveyor 2% so that the strands S are suspended between the open mold ends 120 and 140 of the mold 100.

After a mold 106 and the head 416 are arranged at the placement station 11 in the above-described manner, the hydraulic cylinders 6 are activated to elevate the mold 101) into engagement with the head 416. As illustrated in FIG. 8, the lengths of reinforcing strands S are thereby emplaced in the desired pattern within the cavity of the mold 100, between the open ends 1211 and 140 of the mold. As explained in copending application Ser. No. 721,793, the mold ends 120 and 1411 can then be closed against the body of the mold 100 to engage with the strands S within the strand chucks 12 6 and 146 provided on the end assemblies. As shown in FIGS. 14 and 15, the chucks 126 and 146 will thereby grip the adjacent free ends of the strands S and maintain the strands in the proper position within the mold 166 during the subsequent operating steps of the system.

Upon completion of the strand placement, the members 424 are retracted from the channels 420 by a suitable actuating mechanism (not shown). The cylinders can then be actuated to lower the mold 104 from the head 416, to return the mold to the saddle 2 on the conveyor The mold 106 is thereby positioned on the conveyor 2 for movement through the subsequent operating stations included in the system. The system in accordance with this invention also includes a strand tensioning station 4511, as illustrated in F105. 9 through 11 of the drawings. The tensioning station 450 includes substations 45t1A-C which operate to apply a selected pretensioning force to each of the reinforcing strands S which are emplaced within the portable molds 1M1The preferred form for the strand tensioning means included in station 450 is fully illustrated and described in the copending application of Messrs. Hidden and Yetman, Ser. No. 721,793.

The station 456 in the exemplary embodiment includes a first tensioning substation 450A, as shown in FIG. 9. Substation 4511A is adapted to apply an axial load to two diametrically opposed strands S, to thereby pretension the two strands. To accomplish the strand pretensioning, a tensioning head (not shown), such as described in the Hidden and Yetman application, is connected to the free ends of the strands S, and actuated to apply a measured axial load to the strands. The strand chucks 126 and 1% on the mold end assemblies 120 and 1411 pip the strands, and maintain the strands in their pretensioned condition, after the force of the tensioning head is released. The substation 4508, as illustrated in FIG. 10, is adapted to apply the same measured pretensioning force to the other two diametrically opposed reinforcing strands S, in the same manner. Again, as fully explained in the Hidden and Yetman application Ser. No. 721,793, the strand chucks 126 and 146 will operate to maintain the strands in their pretensioned condition after the tensioning operation of substation 450B is completed.

Referring to FIG. 11, the exemplary embodiment of the tensioning station 450 also includes a substation 450C adapted to apply a final tensioning force to the reinforcing strands S. As

explained fully in the copendirigI-Iidden and Yetman applica- 1 tion Ser. No. 721 ,793, the final tensioning of the strands is carried out to compensate for the pretensioning force lost as a result of the seating of the chucks 126 and 146 on the ends of the strands S. Preferably, substation 450C applies a load to the four strands S simultaneously, to elongate the strands an additional measured amount. The final pretensioning force in the strands S is thereby applied with a high degree of accuracy.

As seen from FIGS. 9.--11, 14 and 15, each substation 450A-C -of the strand tensioning station 450 includes a pair of elevator platforms 452A-C, respectively. As in the operating stations described above, the platforms 452A--C are adapted to raise the molds from the conveyor 2110 so that operation of the substations can be performed. Accordingly, the elevator platforms 452A-C have roller beds 454 for receiving the molds 100, and are joined to hydraulic lift cylinders 456. Guide rods 458 control the positioning ofthe elevator platforms 452A-C and brackets 462, supported on transverse beams are provided to control the longitudinal position of the molds 100 at each of the substations 450A-C. Finally, each substation 450A-C includes a cam track 460, mounted on the respective elevator platforms, for controlling the transverse positioning of the molds 101) at the substations.

A suitable mechanism by which the final tensioning may be applied to the strands S at substation 450C is illustrated in FIGS. 14 and 15 of the drawings. As shown'therein, the substation 450C can be provided with a bifurcated tensioning head which is mounted upon the elevator platform 452C and adapted for engaging the adjacent end plate 142 of the mold 100. The tensioning head 160 has a hydraulic power cylinder 166 connected to a pulling fork 168. The fork 168 is positioned for engagement with a pulling post 148, connected to the adjacent chuck plate 144 of the mold end assembly 141). Since the strands S are engaged within the strand chucks 126 and 146, which in turn are joined to the chuck plates 124 and 144, it is apparent that an outward pull by the power cylinder 166 (rightward in FIGS. 14 and 15) will apply a tensioning force to the strands S. The engagement between the head 160 and the adjacent end plate 142 assures that the mold 106 will not shift during the operation of the power cylinder 166.

When the manufacturing system in accordance with the present invention is in continuous operation, a mold 1611 will be positioned at each of the substations 450A-C of the station 450, and the operations of the substations will be performed simultaneously. However, for simplicity, the operation of the strand tensioning station 450 will be described with reference to the movement of a single mold 100 through the substations. v

To begin with, a mold 106 having the strands S emplaced therein is carried by the conveyor 2% to the substation 450A (FIG. 9). The action of the conveyor 2% places the mold 161) on the roller beds 454 of the elevator platforms 452A. The motion of the conveyor 2611 also brings the mold 160 into engagement with the cam tracks 4611, thereby aligning the mold in the desired transverse position at the substation 450A. The cylinders 456 can then be actuated to raise the mold into the operating position illustrated in FIG. 9. The brackets 462 align the mold longitudinally as the mold rises. As explained in the Hidden and Yetman application Ser. No. 721,793, a tensioning head (not shown) can then be secured to two of the strands S, and operated to apply a measured pretensioning load to such strands. The strand chucks 126 and 146 (FIGS. 14 and 15) seat against the two strands and maintain the strands in a pretcnsioned condition.

After the tensioning operation is completed at substation 450A the actuation of the cylinders 456 is reversed to lower the mold 100 onto the conveyor 2011, within the saddles 264. The mold 100 is next carried to the substation 4508. The substation 450B operates in the same manner as substation 456A to raise the mold 100 into the elevated position shown in FIG. 10. A tensioning head (not shown) is then activated to apply the same pretensioning load to the other opposed strands S.

Again, the chucks 126 and 146 (FIGS. 14 the strands S and maintain the strands in a pretensioned condition.

Upon completion of the tensioning operation at substation 4508, the mold 110 is again lowered into the conveyor saddles 204 and carried by the conveyor 200 toward substation 450C. As shown by the phantom lines in FIG. 14, the elevator platforms 452C at substation 450C are initially positioned in alignment with the conveyor roller beds 208. The action of the conveyor 200 will thereby place the mold 100 onto the elevator roller beds 454, and the adjacent mold end assembly 140 will project into the bifurcatedtensioning head 160. The cam tracks 460 position the mold 100 transversely so that the head 160 engages with the adjacent mold end plate 142 and the post 1418 engages with the pulling fork 168, such as shown in solid lines in FIG. 14. As explained in the Hidden and Yetman application, the cam tracks 460 (FIG. 14) also maintain the locking plates 130 and 150 of the mold end assemblies 120 and 140 in a selected position, so that the previously applied pretensioning force is maintained in the strands S.

Next, the cylinders 456 at substation 450C are actuated to elevate the mold 100 above the conveyor 200. As the mold rises, the brackets 462 engage with the mold and assure that the mold is in a selected longitudinal position. The power cylinder 166 on the tensioning head 160 is then activated to create a pulling force on the mold end chuck plate 144 through the pulling post 148 and fork 168. Since the strands S are secured in the chucks 146, this action of the cylinder 166 further separates the chuck plate 144 from the adjacent end plate 142 and applies an additional pretensioning load to the strands. As mentioned in the Hidden and Yetman application, the pull of the power cylinder 166 is applied to the strands S until the strands have been stretched or elongated a measured amount. Then the locking plate 150 is raised by a hydraulic ram 170 (FIG. 14) into engagement between the separated end plate 142 and chuck plate 144, thereby maintaining the strands in their elongated condition. The pull of power cylinder 166 can then be released, and the lift cylinders 456 can be actuated to return the mold 100 to the conveyor 200.

The mold 100 is thereby provided with pretensioned reinforcing strands, and is ready for conveyance to the subsequent operating stations of the system. Of course, it will be ap preciated by those skilled in the art that the functions of substations $501K and 4503 could be combined at one substation, or a single tensioning head could be employed to applya force-measured pretensioning load to all of the strands S simultaneously, without departing from the present invention. Further, as explained in the Hidden and Yetman application Ser. No. 721,793, the substation 450A and 4503 could be bypassed and only an elongation-measured pretensioning load could be applied to the strands by a mechanism similar to sub station 45%.

The next operating station spaced along the path of the conveyor 200 is a mold filling station 500, as illustrated in FIGS. 12, 16 and 17. The mold filling station 500 is adapted to charge a measured amount of fresh concrete mixture into the cavity of each of the portable molds 100. Further, the mold filling station includes means for vibrating the molds 100 as the charge of concrete mixture is being fed into the mold cavity. Such vibration will tend to compact the concrete, and will assure that the concrete will be uniformly distributed throughout the mold cavity around the inserts 370 and the reinforcing strands S.

Referring to FIGS. l2, l6 and 17 of the drawings in more detail, the station 500 is provided with a charging hopper 516, suspended above the conveyor 200 upon a transverse supporting beam 514. In the illustrated embodiment the charging hopper 516 comprises a pair of mating channel members 518 which together define a hopper cavity of a predetermined volume. In the preferred arrangement the volume of the hopper 516 is chosen to be equal to the volume of the cavities in the molds 100 so that'the hopper can contain the exact volume of concrete mixture needed to fill one of the molds and seat with 100. As seen in 'FIG. 17, the channel members 518 in the preferred embodiment are also preformed so that the hopper 516 will temporarily store the concrete mixture in a distribution pattern which closelycoincides with the pattern of concrete distribution within the cavity of the molds 100. Thus, since the concrete tie being cast by the exemplary embodiment of the system includes a restricted central portion (see FIG. 39) the members 518 include restricted central portions 518A (FIG. 17). I

Moreover, each channel member 518 is rotatably supported on the beam 514 by means of a shaft 520 and bearing block 522. By this arrangement the members 518 can be selectively rotated about the shafts 520 by a suitable control mechanism (not shown), between a closed position, as shown in full lines in FIGS. 12 16 and 17, and an opened position, as shown by the phantom lines in FIG. 12. In the closed position the members 518 engage to form the hopper 516 for storing the concrete charge. In the opened position the members 518 define a discharge chute through which the stored concrete charge will be fed into the cavity of the mold which is positioned at station 500. Any suitable feeding mechanism, such as a feeding chute 524 schematically shown in FIG. 12, can be employed to periodically fill the charging hopper 516 with a measured volume of concrete mixture during the operation of the station 500.

The station 500 also includes a pair of elevator platforms 502 for raising the portable molds 1100 from the conveyor 200 during the mold filling operation. As illustrated in FIGS. 12 and 16, the platforms 502 are positioned in transverse alignment adjacent the conveyor 200, and include roller beds 504 for engaging with and supporting the molds at the station 500. Further, each platform 502 is mounted upon a plurality of springs 505 which project upwardly from a rigid plate 503. Thus, the platforms 502 are freely suspended at the station 500, and can be used for vibrating the molds 100 during the filling operation. To accomplish such vibrating movement, each platform 502 is coupled with a vibrator mechanism comprising an eccentric shaft 507 and a drive motor 509. The motor 509 is connected to the shaft 507 by suitable means such as a belt and pulley arrangement and will operate to rapidly rotate the shaft 507, thereby vibrating the platform 502 on the springs 505. Suitable means (not shown) can be provided to energize the drive motors 509 at the desiredtime during the operation of the station 500.

The station 500 also includes hydraulic cylinders 506, connected to the plates 503, for elevating the molds 100. Guide rolls 508 are also provided to control the positioning of the platforms 502 during the operation of the hydraulic cylinder 506. As in the elevator mechanisms positioned at the other operating stations described above, the platforms 502 also include cam tracks 510 for positioning the mold 100 transversely, and the station 500 includes brackets 512, as shown in FIGS. 12 and 16, for aligning the molds longitudinally.

To begin the operation of the mold filling station 500, a mold 100 is carried from the tensioning station 450 (FIGS. 9- -l1) to station 500 by means of conveyor 200. The cylinders 506 are controlled so that the elevator roller beds 504 initially are aligned horizontally with the conveyor roller beds 208. Thus, the conveyor 200 will drive the mold 100 onto the beds 504, and the cylinders 506 can be actuated to elevate the mold 100 toward the hopper 516 (FIGS. 12 and 16). During these operations, the mold 100 is aligned transversely by engagement with the cam tracks 510 and is aligned longitudinally by engagement with the brackets 512. Also, a measured volume of concrete mixture is fed through the chute 524 into the hopper 516 with the channel members 518 closed, as shown in FIG. 12.

After the mold 100 is elevated into a position such as illustrated in FIGS. 12 and 16, and the hopper 516 has been filled, the station 500 is in condition to charge a measured volume of concrete mixture into the cavity of the mold. The motor 509 can then be energized to rotate the eccentric shaft 507, to thereby. vibrate the elevator platforms S02 and the mold 100. 

1. Apparatus for making prestressed concrete members comprising a plurality of hollow portable molds each defining a mold cavity and including gripping means to receive and releasably grip reinforcing strand placed within the mold cavity, conveyor means to move said molds along a predetermined path of travel successively through a plurality of operating stations positioned along said path, the stations including a mold cleaning station, a mold oiling station, a strand placement station to place reinforcing strand in a selected position within each mold cavity, a strand tensioning station to apply a selected external pretensioning load to said strand emplaced with each mold cavity, with said gripping means engaged with said strand to substantially maintain said external pretensioning load, a mold filling and compacting station, a tension releasing station including a releasing head engageable with said molds to disengage said gripping means from the associated strand and thereby release said external pretensioning load after the concrete in said mold cavity is cured, and a demolding station to discharge the cured concrete members from said molds after said external pretensioning load has been released from said strand.
 2. Molding apparatus in accordance with claim 2 including elevator means at each station to elevate said molds above said conveyor means during the operation of said stations, positioning means to orient said elevated molds into a selected position at each station, and means controlling said elevator means to operate said stations simultaneously.
 3. The invention in accordance with claim 2 wherein said mold elevator positioned at said mold filling and compacting station includes vibrating means adapted to vibrate each of said molds as said mold is charged with said concrete mixture, and thereby facilitate the mold filling operation.
 4. The molding apparatus in accordance with claim 4 wherein said tensioning station includes a tensioning head which applies a selected external pretensioning load to said strand by applying a measured tensioning force directly to said strand.
 5. The molding apparatus in accordance with claim 1 wherein said tensioning station applies a selected pretensioning load to said strand by elongating said strand by a predetermined distance.
 6. In a system for manufacturing prestressed concrete members, the combination comprising: a plurality of portable molds, each of which includes a hollow mold body defining a mold cavity for forming a prestressed concrete member and having an open portion through which said concrete member can be discharged from said mold cavity, each of said molds further including strand gripping means releasably engageable with reinforcing strand emplaced within said concrete member through which an external pretensioning load can be applied to said strand; means to support a plurality of said portable molds in longitudinally spaced relationship and operable to carry said filled molds along a selected path of Travel; and a tension releasing station to successively release the external pretensioning load on said strand after said strand is cast within each of said concrete members, said releasing station including a releasing head successively engageable with each of said molds at said releasing station to disengage said gripping means of each of said molds from the associated reinforcing strand to thereby release the external pretensioning load applied thereto.
 7. A system in accordance with claim 6 wherein each of said molds includes movable ends joined to said body and movable between an open position with respect to said body and a closed position engaged with said body; wherein said strand gripping means are positioned on said movable ends and operable to apply an external pretensioning force to the associated strand when said mold ends are in said closed position and to disengage the strand when the mold ends are in said open position; and further wherein said tension releasing head engages with and releases said gripping means and permits the removal of the strand from said gripping means by movement of said mold ends into said open position.
 8. A system in accordance with claim 7 wherein said tension releasing head includes means to engage with and release said gripping means and means engageable with said mold ends to translate said mold ends from said closed position to said open position and thereby remove the strand from said gripping means.
 9. In a system for manufacturing prestressed concrete members, the combination comprising: a mold body defining a hollow mold cavity; a mold end assembly movable between a closed position engaged with said mold body and an opened position spaced from said body; said end assembly including an end plate engageable with said body, a chuck plate aligned with and movable with respect to said end plate, strand gripping means on said chuck plate, grip releasing means, and locking means positioned between said end and chuck plates and operable to maintain a pretensioning load in strand engaged by said gripping means by spacing said chuck plate a predetermined distance from said end plate; and a releasing head for selectively releasing the strand pretensioning load; said releasing head comprising force-applying means engageable with said end and chuck plates to separate said plates and release said locking means; means to engage said strand gripping means with said grip releasing means to deactivate said gripping means; and means to translate said end assembly from said closed position to said opened position to disengage said gripping means from the reinforcing strand.
 10. In a system for manufacturing prestressed concrete members, the combination comprising: a plurality of molds each including a mold body defining a hollow mold cavity having an opened top portion and movable mold ends slidably connected to said mold body; strand gripping means on said mold ends to releasably grip reinforcing strand and apply an external pretensioning force thereto; first conveyor means to carry said molds along a selected path of travel; a tension releasing station positioned adjacent said first conveyor, said releasing station including a releasing head positioned above said first conveyor and operably engageable with the movable mold ends to successively disengage said gripping means from the free ends of the associated reinforcing strand, thereby releasing the external pretensioning load applied to the strand, and to translate said movable mold ends outwardly into an open position with respect to the body of the associated mold beyond the length of said free ends of said strand; mold elevator means to receive said molds as said molds are carried to said releasing station by said first conveyor and operable to successively engage said molds with said releasing head; positioning means at said tension releasing station to orient said molds into a selected position with respect to said releasing head; sEcond conveyor means positioned downstream from said tension releasing station engageable with said opened mold ends to support a plurality of said molds and the associated concrete members cast therein; means to successively transfer each of said molds from said first conveyor to said second conveyor in an inverted position; supporting means extending along said second conveyor for a selected distance to support the concrete members within said inverted molds as said molds are carried by said second conveyor; a demolding station positioned along the path of said second conveyor to successively discharge the concrete members from said inverted molds, said demolding station including a platform movable into alignment with said supporting means to successively receive and support concrete members as the associated inverted mold becomes positioned at said demolding station, said platform being further movable to successively lower said concrete members between the opened movable ends of the associated mold; means positioned adjacent said demolding station to receive and support said demolded members; and a finishing station to successively finish each of said demolded concrete members, said finishing station including cutting means to sever the projecting free ends of reinforcing strand from each of said members.
 11. The invention in accordance with claim 1 wherein said mold cleaning and oiling stations include a collection head to collect and remove the dust and debris loosened from each of said mold cavities and an oiling head to apply a coat of releasing agent to the cleaned interior wall portions of each of said mold cavities.
 12. The invention in accordance with claim 1 wherein said mold filling and compacting station includes a filling head formed to store a measured volume of concrete mixture in a distribution pattern which substantially coincides with the predetermined distribution pattern for said concrete mixture within the cavity of each of said portable molds.
 13. In a system for manufacturing prestressed concrete members, the combination comprising; a plurality of portable molds, each of which includes a hollow mold body defining a mold cavity filled with a cured prestressed concrete member and having an open portion through which said cured concrete member can be discharged from said mold cavity, each of said molds further including strand gripping means releasably engaged with reinforcing strand cast within said cured concrete member through which an external pretensioning load is applied to said strand; means adapted to support a plurality of said filled portable molds in a longitudinally spaced relationship and operable to carry said filled molds along a selected path of travel; a tension releasing station to successively release said external pretensioning load on said strand cast within each of said concrete members, said releasing station including a releasing head successively engageable with each of said molds at said releasing station and further being operable to disengage said gripping means of each of said molds from the associated reinforcing strand to thereby release the external pretensioning load applied thereto; means positioned adjacent said tension releasing station to successively receive said filled molds and engage said molds with said releasing head; positioning means arranged at said tension releasing station to engage with and orient said molds into a selected position with respect to said releasing head; support means positioned downstream from said tension releasing station to support a plurality of said filled molds in a longitudinally spaced relationship with said gripping means disengaged from said reinforcing strand; a demolding station to successively discharge said cured concrete member from each of said filled molds, said demolding station including positioning means engageable with each of said molds and the associated concrete member to maintain said molds and Concrete members in selected positions at said demolding station; demolding means successively engageable with each of said cured concrete members as each of said filled molds is successively carried to said demolding station to separate said cured concrete member from the mold positioned at said demolding station, to thereby discharge said members from said molds; and member-supporting means positioned adjacent said demolding means at said demolding station to receive each of said cured concrete members after said members are discharged from the associated portable mold.
 14. The invention in accordance with claim 13 wherein said demolding means comprises an elevator mechanism positioned at said demolding station and wherein said member-supporting means comprises a conveyor positioned adjacent said elevator mechanism, said elevator mechanism including a platform movable into alignment with said support means to engage with the cured concrete member associated with a mold as said mold becomes positioned at said demolding station, said elevator platform being further movable to transfer a cured concrete member to said conveyor, so that the controlled movement of said elevator platform removes the concrete member engaged with said platform from the associated mold and transfers said member to said conveyor.
 15. The invention in accordance with claim 14 wherein said system includes a finishing station positioned adjacent said conveyor to successively receive said cured concrete members demolded at said demolding station, said finishing station including strand cutting means to sever said strands from said cured concrete members as said members are carried through said finishing station.
 16. The invention in accordance with claim 13 wherein said system includes mold turnover means positioned adjacent said support means downstream from said demolding station, said turnover means including a rotatable turnover head which is movable into alignment with said support means to successively receive empty molds from said demolding station, said turnover head being further rotatable into a position which inverts said empty molds received therein so that said empty molds are successively positioned with the open portions of said molds directed upwardly, whereby said turnover station orients said molds for recycling through said manufacturing system. 